1. Field of the Invention
This invention relates to a driving apparatus of a display panel having capacitive discharge cells.
2. Description of the Related Art
A plasma display apparatus having an AC discharge type plasma display panel mounted thereto as a thin display device is known.
The AC discharge type plasma display panel (hereinafter called “PDP”) includes a plurality of column electrodes and a plurality of row electrode pairs so arranged as to respectively intersect the column electrodes while interposing discharge spaces having a discharge gas sealed therein among them. A discharge cell emitting red light, a discharge cell emitting green light or a discharge cell emitting blue light at the time of its discharge is formed at each point of intersection between each row electrode pair and each column electrode inclusive of the discharge space.
Because the discharge cell causes light emission by utilizing the discharge phenomenon, it has only two states, that is, a “light-on state” in which the discharge cell emits light at predetermined luminance, and a “light-off state”. In other words, the discharge cells can provide luminance of only two gradations. To achieve luminance display of an intermediate tone corresponding to input image signals by using such discharge cells, a driving apparatus for executing gradation driving in accordance with a sub-field method is disclosed in JP-A-2000-338932.
The sub-field method divides a display period of one field into N sub-fields and allocates in advance periods in which each discharge cell is allowed to continuously emit light (or to be turned off) to each sub-field. Each discharge cell is allowed to emit light or is turned off in accordance with the input image signal for each sub-field for the period allocated to the sub-field. It becomes possible in this way to express various kinds of intermediate luminance of 2N stages (N: number of sub-fields; hereinafter called “gradation”) through combinations of the sub-fields that are to emit light during one-field period.
To accomplish gradation driving on the basis of the sub-field method described above, a driving apparatus (not shown in the drawings) applies various driving pulses to the PDP and causes various discharges in the discharge cells. In other words, the driving apparatus first applies a reset pulse to the row electrode pairs of the PDP and induces reset discharge in all the discharge cells. A predetermined quantity of wall charge is uniformly formed in all the discharge cells due to this reset discharge. Next, the driving apparatus causes serially and selectively erase discharge of the discharge cells in accordance with the input image signals for one horizontal scan line (hereinafter called “one display line”). In this instance, the wall charge remaining inside the discharge cells disappears in those discharge cells in which the selective erase discharge is induced. In those discharge cells in which the selective erase discharge is not induced, on the other hand, the wall charge created by the reset discharge remains as such. Next, the driving apparatus alternately and simultaneously applies sustain pulses the number of times corresponding to each sub-field to all the row electrode pairs. Only those discharge cells in which the wall charge remains repeatedly cause the sustain discharge for the period corresponding to the sub-field in accordance with the application of such sustain pulse and keep the light emission state resulting from this sustain discharge.
In the PDP, however, the quantity of the wall charge created by various kind of discharges does not-remain constant due to the temperature change of the panel, the shift of display luminance, the change with time, and so forth. For this reason, the PDP involves the problem that variance occurs in the intensity of discharge and display quality gets deteriorated.
To solve the problems described above, the invention aims at providing an apparatus for driving a display panel that can always execute quality image display.